There are transmission methods for improving frequency usage efficiency known heretofore, including for example, methods for transmitting symbols of bock units using multiple antennas, such as with space-time block codes. This technique is disclosed, for example, in “Space-time Block Codes from Orthogonal Designs,” IEEE Transactions on Information Theory, pp. 1456-1467, vol. 45, No. 5, July 1999. The content of this non-patent document 1 will be described below with reference to the accompanying drawings.
As shown in FIG. 1, a transmitting apparatus has multiple antennas AN1 and AN2 and transmits signals at antennas AN1 and AN2 simultaneously. A receiving apparatus receives the multiple signals, transmitted simultaneously, by means of antenna AN3.
FIG. 2 shows the frame configuration of the signals transmitted at antennas AN1 and AN2. Transmission signal A is transmitted at antenna AN1 and at the same time transmission signal B is transmitted at antenna AN2. Transmission signal A and transmission signal B consist of symbol blocks, where the same symbols are arranged in repetition so as to achieve coding gain and diversity gain.
This will be explained in further details. In FIG. 2, S1 and S2 represent different symbols and the asterisk (“*”) represents the complex conjugate. In space-time block coding, at time i, symbol S1 is transmitted at first antenna AN1, and, at the same time, symbol S2 is transmitted at second antenna AN2. Subsequently, at time i+1, symbol −S2* is transmitted at first antenna AN1 and at the same time symbol S1* is transmitted at second antenna AN2.
At antenna AN3 at the receiving apparatus, the signal combining transmission signal A, which has been influenced by channel fluctuation h1(t) between antenna AN1 and antenna AN3, and transmission signal B, which has been influenced by channel fluctuation h2(t) between antenna AN2 and antenna AN3, is received.
The receiving apparatus estimates channel fluctuation h1(t) and h2(t), and, utilizing the estimated values, separates the received composite signal back to original transmission signal A and transmission signal B and thereafter decodes the individual symbols.
Thereupon, the use of space-time block coded signals such as shown in FIG. 2 makes possible maxim ratio combining of symbols S1 and S2 in spite of channel fluctuation h1(t) and h2(t), so that excellent coding gain and diversity gain are achieved. As a result, it is possible to improve reception quality.    Non-Patent Document 1: “Space-Time Block Codes from Orthogonal Designs,” IEEE Transactions on Information Theory, pp. 1456-1467, vol. 45, No. 5. July 1999.